Putting forward in recent years, the Software defined radio (SDR) technology is a new architecture for implementing wireless communication. It is mainly directed at some problems existing in the field of wireless communication, such as coexistence of multiple communication systems, fierce competition between various standards, and shortage of frequency resources. In particular, the development of wireless private communication systems results in that new systems are emerging one after another, product periods get shorter and shorter, it is hard for the previous wireless communication system relying mainly on hardware to be suited to such a situation, and thus, the concept of Software defined radio emerges as the times demand. Generally speaking, Software defined radio is an architecture that connects modularity and standardization functions of software together via a universal platform and is capable of accomplishing various wireless communication systems through software loading. Software defined radio achieves various functions in a wireless communication system by means of software, which is another revolutionary leap following the transition of radio station from analogue to digital. Software defined radio is even regarded as a super computer with antennas, which is capable of adjusting and changing a station's work frequency band, modulation and demodulation system, coding and decoding form, service type, data speed and format, encrypting mode, access control protocol etc by re-structuring and controlling software modules. A software module is comprised of various software algorithm libraries. By loading software algorithm or updating software version, the expansion function of services is achieved and a new communication standard can be employed.
Due to the characteristics of software per se, wireless communication system and apparatus based on the SDR technology is endowed with the following capabilities:
1. Capability of Reprogramming/Reconfiguring
SRD apparatus can be reprogrammed and reconfigured in a fast and simple way so as to support the application in various transmission fashions and the transmission or receiving at any frequency; the capability of reprogramming and reconfiguring results in the fact that an identical device supports different cell technologies, private communication systems and other wireless services applied in a worldwide scale.
2. Capability of Providing and Changing Services
By adopting a SDR apparatus, a user can use both traditional and new services; and the concept of air-loading software can guarantee the user the acquisition of the latest service.
3. Capability of Supporting Multiple Standards
SDR enables a wireless operator to achieve the system's version updating, standard updating etc without changing hardware of a base station. Additionally, a new wireless communication system is defined by software.
As seen from the current situation, various standards of the 3rd generation mobile communication system (WCDMA/CDMA2000/TD-SCDMA)will coexist. Thus, the development & research on a multi-standard mobile communication system/apparatus will greatly benefit manufacturers, operators and users. Such a multi-standard mobile communication system/apparatus uses a public hardware platform and achieves different functions/standards by loading different software. After a standard is upgraded, the whole communication system/apparatus can support the new standard simply by upgrading software correspondingly. Hence, it is of practical significance to research into the software framework, designing and development method of multi-standard SDR.
SDR software can be divided into control software and protocol software. Control software mainly performs the function of control, such as performing configuration, setting, management and the like with respect to a base station; while protocol software mainly realizes the function of the protocol corresponding to each standard. The SDR software framework shall possess the following properties                Flexibility: possibility of processing multiple modes, multiple frequency-bands, multiple standards etc;        Reconfiguration: must being compatible with the existing main standards and capability of being upgraded in accordance with the standard conceivable in the future; Upgrading an identical standard and changing various standards can be achieved through reconfiguration;        Reusability: a software module should being reusable as much as possible. Different standards use an identical control module in the control part; and modules of similar functions are reused as much as possible in the protocol software part.        
Currently there are two typical SDR software frameworks: one is SCA-based software framework adopted by SDR forum, the other is CCL/ITRI SDR software system.
1. SCA-based SDR Software Framework
At present, Software defined radio (SDR) forum prefers to use Common Object Request Broker Architecture (CORBA) platform and employ Software Communication Architecture (SCA) as the standard of software framework of SDR system. SCA provides a framework of SDR apparatus software which succeeds in using Common Design patterns. The software of SDR apparatus is comprised of control program and wireless application program. By taking CORBA as middleware, SCA provides a flexible environment for integrated dissimilar hardware and software written by multiple languages. As a standard developed for Joint Tactical Radio System, SCA employs CORBA for its distribution object structure, which leads to object-request broker (ORB) become a basic comprising part thereof. The interfaces of the object use interface definition language (IDL), and unified modeling language (UML) is used for illustrating an application example.
2. CCL/ITRI SDR Software Frameworks
Computer & Communications Research Labs/Industrial Technology Research Institute (CCL/ITRL) SDR software system is developed by CCL/ITRI. Providing an effective SDR software framework for CCL/ITRI SDR hardware, this framework can be realized both at terminal and base station sides, with the function including bootstrap of SDR system, stop of SDR system, configuration of SDR system, switching of SDR system mode and the like. In order to satisfy these high-level functional requirements of SDR system, this software architecture is divided into 6 parts which are: SDR kernel framework (SDR_CF), SDR software module manager (SDR_SMM), SDR software module, SDR hardware abstract layer (SDR_HAL), SDR hardware manager (SDR_HM) and SDR hardware module (SDR_HWM). This framework not only needs to be integrated with CCL/ITRI SDR hardware platform, but also shall be implemented in commercial off the shelf (COTS) operating system.
However, the existing art has the following disadvantages.
1. SCA
SCA system is applicable to the designing of relatively high-level software other than to base-band software. The initial purpose of developing SCA is for military radio system. Due to its military background, SCA has features that are not required for commercial application. As a mature structure CORBA is, it brings about problems in performance and flexibility to SDR system. High performance is vital to base-band software, whereas most of advantages provided by CORBA are of no use to base-band software. Therefore, the development of base-band software is generally not based on CORBA platform. Usually SDR hardware does not provide CORBA environment, thus resulting in a big problem in implementing CORBA.
2. CCL/ITRI SDR Software Systems
This software system is specially used for the hardware platform designed by CCL/ITRI. Moreover, software module of this software framework needs to be implemented within the kernel of operating system. Therefore, this software framework is not in common use.
The existing two SDR software frameworks put more attention to control part, but less involves software framework and method for designing and developing of protocol part.